Speed selector with delayed temperature datum adjustment



Nov. 7, 1961 J. SKELLERN 3,007,307

SPEED SELECTOR WITH DELAYED TEMPERATURE DATUM ADJUSTMENT Filed May 14,1957 TORQUE saws/N6 2 DEV/CE I, 7-0 55%? R UNIT 53 rempsm mes 28 CONTROLu/vlT 55 FUEL EE Tl/EN 4 S 'Pzsssumso FUEL 4a 52 49 F762. J

"gi -ff? V 3 0 INVENTOR JouN SkEu-ERN MM M, M1!- Awwoenevs United Thisinvention relates to control systems for variable speed gasturbinepower'u'nits, of the kind in which there is a temperature-sensingdevice for sensing the turbine inlet temperature and arranged toinfiuenc'e the supply offuel to'the power unit in the eventof therebeing a difference (herein termed anerror) between the datum temperatureto which the temperature sensing device is set and the apparenttemperature" at the turbine inlet as sensed by the devicefthe efiect onthe fuel-supply being" an adjustment thereof tending to eliminate theerror. Such temperature-sensing devices are. commonly used in gasturbine power units for ensuring that the turbine is not overheated.

This application is a' continuation in part of my copending application#548,506 filed November 22 1955 now a U.S. Patent #2,802,335 grantedAugust '13, 1957.

In some cases the maximum permissible temperature at the turbine inletis different at diiferent speeds. In such cases a variable datumtemperature-sensingdevice may be provided, the adjustment ot 'the datum=being effected by a speed selector member ofthepower unit which alsoadjuststhe fuel supply to produce any desired change in speed. 7

Temperature sensing devices are not instantaneous in their response tochanges inthe actual temperature being sensed, due largely to the heatcapacityof the part that is exposed tothe'temperature being sensed.Consequently, in the event of' the speed selector member being suddenlymoved to increase the actual temperature at the turbine inlet and toincrease the datum, the actual temperature at the turbine inlet mightrise substantially above the new datum by the time the apparenttemperature as sensed by the device begins to exceed the new datum andtheresulting error between the'datum-andthe apparent temperature causesthe device to reduce the fuel supply. Conversely, in the event of thespeed selector member being suddenly moved to reduce the actualtemperature at the t-urbi'ne'inlct and to reduce the datum, the apparenttemperature as sensed by the device might still be above the new datumwhen the temperature at the turbine inlet had fallen to or below the newdatum, and the error between the datum and the apparent temperaturewould cause the device to operate to reduce the fuel supply below'whatwas actually required to maintain the actual turbineinlet temperature atthe new datum. This might in some cases cause flame extinction orstalling of the compressor. These undercorrectionsand" over correctionsof the'fuel' supply by the temperature-sensing device may also causehunting of the fuel regulation.

It is an object of the present invention tominimize or overcome-thesedisadvantages According to the present invention, inacontrol system-ofthe kind specified which includes means actuated by the speed selectormember of the power unit foradjustingthe datum of thetemperature-sensing device in accordance with changes irr selectedspeedof thepower' unit, a delay device is provided between the speedselector'memher and the datum adjustment.

In one form of the inventionthe characteristics of the delay device aresuch that adjustments of the datum in response to movements of thespeedselector member approximately coincide with the response of thetemperrates Patet 3,007,307 Patented Nov. 7, 1961 "ice Thus, inthe eventof the speedselector member being;

moved to adjust the fuel supply to provide; a change of speed, the datumof. the temperature-sensing device will also be adjusted but moreslowly, with a delay corresponding approximately with the delay in theresponse of. the temperature-sensing device, so that although the ac.-tual temperature at the turbine inlet will change quickly as a' resultin: the. change in the fuel supply while the apparent temperature assensed by the temperaturesensitive device changes at a slower rate,there will not be a material error between this. apparent temperatureand: the datum temperature because the datum temperature willalsochangeat about the same slow rate. By'timing the adjustments in thedatum to coincide with the changes inthe apparent temperature'a's sensedby the-device instead of with the changes in' the actual temperature-atthe turbineinlet', under-corrections or over-correctionsrof the'fuelsupply by the temperature sensing device arevirtually eliminated.

In another form of the invention the characteristics of thedelay deviceare such that adjustments'ot the datum in response to movements of thespeed selector member lag behind the response of thetemperature-sensingdevice to changes in the turbine inlet temperatureresultingjfrom such'movements, toprovide anacceleration control;

Thus if, during a selected acceleration ofthe power unit, the actualturbinein'let temperature: hasv attained .a particular value, theapparent temperature as sensed by the temperature-sensing device hasattained some'ilower value, and the datum setting of the temperaturesensing device isat a-still lower value owing to-its greater. time lag,the error between the datum temperatureof the temper.- ature sensingdevice and the apparent temperature sensed by the temperature sensingdevice will reduce the fuel supply to the engine and so arrest andcontrol the rate of power unit acceleration;.

Ina control: system in which the movements of the speed selector memberare transmitted to the datum adjustment through a servo motor it isconvenient toincor porate the delay device in the servo motor. Forinstance, a hydraulic servo motor may be provided with restrictors inthe flow passages for the actuating fluid to. retard the rate of flow.

The present invention may be incorporated in various type of controlsystem, and may be fitted with various refinements to suit specialrequirements. For instance, in one form of control system for anaircraft power installation containing a plurality of gas turbine powerunits provision is made, in the event of failure of a power unit, forthe remaining power unit or units automatically to be set to produce anabnormally high emergency power output. This requires the temporaryelimination of the influenceofthe turbine inlet temperature-sensingdevice of any power unit set to produce the emergency power output. Inone formof the invention applied to such a control system thetemperature-sensing device influences the supply of fuel to the powerunit by means of a bleed valve, and the system includes means wherebythe bleed valve can be maintained in the closed position to eliminatethe influence ofthe temperature-sensing device.

The invention maybe performed in various ways, and one particular form.of gas turbine control system em- ;bodying the invention will now bedescribed by way of eirample' withv reference to the accompanyingdrawings in which:

FIGURE: 1' .is a diagrammatic. view of' the. power unit showing certainelements of itss-con'trol' system; and

FIGURE 2' is a; diagrammatic view of the temperaturesensing device forsensingthe turbine inlet temperature. The gas turbine power unit 10shown in FIGURE 1 is intended for driving one rotor 11 of a twin rotorhelicopter, a second rotor being driven by a similar power unit which isnot shown. The power unit comprises a vertically mounted axial flowcompressor 12 which draws in air through an inlet 13, compresses thisair and discharges it into combustion chambers 14 wherein the airsupports the combustion of a metered quantity of fuel injected throughburners 15. The hot gases are expanded through a compressor-drivingturbine and a power turbine contained in a turbine casing 16 and areexhausted to the atmosphere through ducts 17. The compressor-drivingturbine drives the compressor 12 through a shaft 18, and the powerturbine drives the rotor 11 through reduction gearing 19 and a shaft 20equipped with a torque-sensing device 21.

The fuel supplied to the burners 15 is drawn from a tank 63 anddelivered by a variable stroke plunger pump 22 through a metering unit23 and a delivery pipe 24. The metering unit regulates the quantity offuel delivered to the burners in dependence on the setting of a speedselector member 25 under the pilots control, and also imparts automaticcorrections to compensate for variables which would afiect the speed ofthe power unit, namely the temperature and pressure of the air enteringthe compressor 12. The speed selector member 25 is connected to themetering unit 23 through a connection 26. If the speed selector member25 were suddenly advanced to increase the speed of the power unit, themetering unit 23 would permit a large quantity of fuel to pass to theburners which might produce an undesirably high temperature at theturbine inlet. To avoid this possibility an additional control isexercised over the metering unit in response to the turbine inlettemperature as sensed by a mercury-filled bulb 27. The control iseffected by means of a temperature-sensing device 28 shown in moredetail in FIGURE 2. This device comprises a Bourdon tube 29 connected bya capillary tube 30 to the bulb 27, a lever 31 having a fulcrum 32 andagainst which the upper end of the Bourdon tube acts, and a half-ballbleed valve 33 against which the free end of the lever 31 bears. Thehalf-ball bleed valve 33 permits metered fuel to bleed off from thedelivery pipe 24 through a pipe 54 and back to the inlet side of thefuel pump 22 through a pipe 65 when the apparent temperature at theturbine inlet rises high enough to cause the Bourdon tube 29 to raisethe lever 31, and so reduces the supply to the burners 15.

At different speeds of the power unit the maximum permissible turbineinlet temperature for normal operation also differs. Consequently it isnecessary for the datum of the temperature-sensing device 28, i.e. theapparent turbine inlet temperature at which the bleed valve 33 opens, tobe varied in dependence on the speed of the power unit. This is effectedby connecting the speed selector -25 to the temperature-sensing devicethrough a connection 34 which determines the position of the fulcrum 32.

The connection 34 carries a cam 35 which is adjustable by means of aclamp 36. The cam acts on a lever 37 which in turn controls a half-ballvalve 38. This valve is mounted in the piston 39 of a follow-up servomotor 40. The space 41 below the piston 39 is in permanent communicationwith a pipe 42 through which fuel under pressure is supplied, and thespace 43 above the piston likewise communicates with the pipe 42 butthrough a fine restrictor 44 so' that fluid can enter the space 43 onlyslowly. The half-ball valve 38 controls the escape of fluid from thespace 43 through a passage 45 and a restrictor 46. The piston areaexposed to the space 43 is greater than that exposed to the space 41 sothat when the half-ball valve is closed the piston 39 slowly descends.If the selector member 25 is moved to cause the cam 35 to permit thelever 37 to tilt clockwise and so permit the half-ba1l valve 38 to lift,fluid will escape from the space 43 permitting the piston 39 to rise byan amount equal to the lift of the half-ball valve 38. Conversely, ifthe selector member 25 is moved in the opposite direction the valve 38is closed and since rfiuid can no longer escape from the space 43 thepiston 39 descends until the valve 38 ceases to follow it. A spring 47interposed between the cam 35 and the lever 37 permits the cam to bemoved in advance of the corresponding downward movement of the piston 39and the valve 38. The movements of the piston 39 are trans mitted to thefulcrum 32 through a lever having an adjustable fulcrum 48, and througha rod 50. Ad ust able abutments 51 and 52 determine the end positions ofthe piston 39.

The lever 31 thus constitutes a difierential mem having three elements,namely the end controlling valve 33, the intermediate point controlledby Bourdon tube 29, and the fulcrum 32, the positions of the last twoelements determining the position of the first element.

The arrangement described ensures that in the event of there being anerror between the datum temperature to which the temperature-sensingdevice is set (i.e. t e position of the fulcrum 32) and the apparenttemperature at the turbine inlet (i.e. the position of the PP end of theBourdon tube 29) an appropriate adjustment of the metered fuel supplywill be effected by the hal ball valve 33. But the apparent temperatureat the am bine inlet will differ from the actual temperature at theturbine inlet when operating conditions are changing rap idly, owing tothermal inertia of the bulb 27. Cause quently a false adjustment of thefuel supply would occur, accompanied by the undesirable effectspreviously mentioned, unless the measures contemplated by the pres entinvention are employed. These measures comprise the incorporation of atime delay into the follow-up servo motor 40 by means of the saidrestrictors 44 and 46. These restrictors are so selected that themovements of the piston 39 in response to movements of the speedselector member 25 are delayed to coincide approximately with thechanges in the position of the upper end of the Bourdon tube 29resulting from changes in the turbine inlet temperature produced bychanges in fuel supply gaused by the said movements of the speedselector mem- Alternatively, by selecting the restrictors 44 and 46 sothat the movements of the piston 39 in response to movements of thespeed selector member 25 lag behind the corresponding changes in theposition of the upper end of the Bourdon tube, the system will providean acceleration selector as previously explained.

The system also includes a refinement to satisfy a re quirement of thisparticular twin-rotor installation. This requirement is that if onepower unit fails the other must be automatically set to produce anabnormally high emergency power output. This entails accepting temporarily an abnormally high turbine inlet temperature. If the saidrefinement were omitted, the system as so far described would operate toprevent the occurrence of this high temperature which would prevent thedesired high emergency power output from being achieved. The refinementoperates to put the temperature-sensitive device of one power unit outof action automatically when the other power unit fails. As previouslyindicated, each power unit transmits its drive through a torque-sensingdevice 21. In the event of the transmitted torque of one power unitfalling to a predetermined value indicative of a failure, thetorque-sensing device 21 thereof sends a signal through a connection 53to actuate an emergency override device 60 of the other power unit. Thepower unit illustrated has an identical override device 60. The overridedevice 60 comprises a valve 61 actuated by a servo motor 62 controlledthrough a connection 53A from the torque-sensing device of the othersaid powerunit. On actuation of the servo motor 62 the valve 61 admitsfluid under pressure into a pipe 55 leading to a space above a piston 56to depress this piston and close the half-ball bleed valve 33irrespective of the position of the lever 31. The temperature-sensitivedevice 28 thereupon ceases to have any influence over the fuel supply.

What I claim as my invention and desire to secure by Letters Patent is:

l. A control system for a variable-speed gas turbine power unit,including a fuel metering unit for metering the fuel supply to said gasturbine means for adjusting he supply of metered fuel to said gasturbine, a temperature-sensing device exposed to the turbine inlettemperature, a differential member having three elements the position ofone of which is determined by the position of the other two, anoperative connection between said one element and said fuel adjustingmeans, a connection between said temperature-sensing device and anotherelement of said differential member whereby the position of this elementdepends on the apparent turbine inlet temperature as sensed by saidtemperature-sensing device, a turbine inlet temperature datum adjustingdevice, an operative connection between said datum adjusting device andthe third element of said differential member, said differential memberinfluencing said fuel adjusting means when there is an error between theturbine inlet temperature datum and the apparent turbine inlettemperature as sensed by said temperature-sensing device, a speedselector member for said gas turbine, a first operative connectionbetween said speed selector member and fuel metering unit, a secondoperative connection between said speed selector member and said datumadjusting device adapted to adjust the turbine inlet temperature datumin accordance with the setting of said speed selec tor member, and atime delay device in said last mentioned operative connection fordelaying the change in adjustment of said datum responsive to a movementof said speed selector member.

2. A control system according to claim 1 in which said operativeconnection between said speed selector member and said datum adjustingdevice includes a fluidactuated followup servo motor and said time delaydevice consists of a fluid flow restrictor incorporated in said servomotor.

3. A control system according to claim 1 in which said means foradjusting the fuel supply comprises a bleed valve adapated to beactuated by said differential member, and the system includesover-riding means adapted when operative to hold said bleed valve closedto permit over-fueling irrespective of the position of said differentialmember.

4. A control system according to claim 1, in which said time delaydevice has an input member and an output member and which includes meansconnecting said speed selector member to said input member whereby saidinput member moves simultaneously with movements of said speed selectormember, and means connecting said output member to said datum adjustingdevice whereby movements of said output member produce simultaneousmovements of said datum adjusting device, said time delay deviceincluding delaying means whereby a movement of said input memberproduces movement of said output member said movements of said outputmemher having a predetermined time delay relationship to said movementsof said input member, and the inherent heat capacity of said temperaturesensing device provides a delayed response characteristic to changes insaid turbine inlet temperature, said delaying means being selected sothat said time delay relationship of said time delay device coincideswith said delayed response characteristic of said temperature sensingdevice.

5. A control system according to claim 1, in which said time delaydevice has an input member and an output member and which includes meansconnecting said speed selector member to said input member whereby saidinput member moves simultaneously with movements of said speed selectormember, and means connecting said output member to said datum adjustingdevice whereby movements of said output member produce simultaneousmovements of said datum adjusting device, said time delay deviceincluding delaying means whereby a movement of said input memberproduces movement of said output member, said movements of said outputmember having a predetermined time delay relationship to said movementsof said input member, and the inherent heat capacity of said temperaturesensing device provides a delayed response characteristic to changes insaid turbine inlet temperature, said delaying means being selected sothat said time delay relationship of said time delay device lags behindsaid delayed response characteristic of said temperature sensing device.

Reterences Qited in the file of this patent (Duplicate of US. Patent No.2,802,335)

